On Thursday, the Centers for Disease Control and Prevention issued a special Zika travel advisory for 11 Southeast Asian countries.

"CDC now recommends that pregnant women should consider postponing nonessential travel to these countries because of the uncertain risk of Zika virus infection," the agency said in a statement.Zika virus has been present in areas of Southeast Asia for many years, and several countries have reported occasional cases or small outbreaks of Zika virus infections. Zika virus is considered endemic in some countries, and a large number of local residents are likely to be immune. However, US travelers to endemic areas may not be immune to Zika virus and infections have occurred among travelers to Southeast Asia.Recent variations have been observed in the number of cases reported in Southeast Asia. This can reflect changes in awareness of Zika virus, surveillance and testing for Zika virus, or changes in intensity of Zika virus transmission. Pregnant women traveling to Southeast Asia could become infected with Zika virus. The level of this risk is unknown and likely lower than in areas where Zika virus is newly introduced and spreading widely.